Patent GB-452136-A (GB)
Title: Improvements in measurement apparatus
IPC: G01R13/00
Filed: 1934-11-15
Abstract: 452,136. Current, pressure, and power meters; resistance and frequency measurements compensating instruments for temperature errors. CHILOWSKY, C., 15, Rue du Lunain, Paris. Nov. 15, 1934, No. 32947. Void [Abridged as open to inspection under Sect. 91 of the Acts, May 16, 1935]. [Class 37] [See also Group XIX] An instrument in which the movable element is immersed in liquid having a density substantially equal to that of the movable element is compensated for temperature variations by compensating the variations of buoyancy of the liquid by expansion of the moving member or of part of the container. As shown in Fig. 1, the movable element consists of a tube 1 of soft iron suspended by a spring 3 within a tube 2 of transparent material and partly projecting into a solenoid 4 carrying the current to be measured. The tube 1 carries at its upper end a part 6, also of soft iron, which carries the magnetic flux passing through the tube and enables the stroke of the movable element to be increased. An index 8 on the part 6 co-operates with a scale 9. In another construction, Fig. 2, the movable element consists of a tube 13 containing two permanent magnets 14, 15 with their poles oppositely arranged so as to form an astatic system. These are acted on by two coils 11, 12 which may be arranged so as to compare resistances 18, 19. If one of these is a photo-electric cell, the apparatus constitutes an exposure meter. In the form shown in Fig. 3 the movable element comprises two small solenoids 21, 21 connected by a tube 22 hydraulically suspended in a tube 23 containing a permanent magnet 24, the magnetic circuit of which is closed through bars 25 outside the tube. The solenoids 20, 21 are spaced apart by half the length of the magnet 24 and are suspended by springs 26, 27 which also serve for leading in the current. In another construction, Fig. 4, the movable element consists of a tube 28 of ebonite about which is wrapped a magnetic sheet 29 which may be slightly deformed so as to permit expansion of the ebonite. The tube 2 is filled with water, the coefficient of expansion of ebonite being the same as that of water. In an alternative method of temperature compensation the tube 2 is provided at its upper or lower end with a bellows 31, Fig. 5, carrying the end of the spring 3. Expansion of the liquid in the tube causes an upward displacement of the movable element 1 which compensates for the downward displacement resulting from the decrease of buoyancy. The movable element may be supported by a spring fixed to the bottom of the tube 2 as shown in Fig. 6, the buoyancy in this case being slightly superior to the weight of the movable element, so that this is urged upwardly in the absence of current in the solenoid 4. The upper end 33 of the element 1 may be illuminated by a small reflector 30, the portion 33 of the element 1 having a conical reflecting surface so as to reflect the light rays laterally and thus. illuminate the scale 9. Alternatively an elongated cylindrical electric lamp 35, Fig. 7, with a straight filament 36, may be mounted parallel to the tube 2 so as to illuminate horizontally the part of the tube in which the upper end of the member 1 moves. The liquid employed may alternatively be a 5 to 10 per cent solution of caustic soda or a 10 per cent solution of methyl alcohol. An organic liquid of high density such as bromoform may be used, the movable element being partly made of a light product such as wax or paraffin having a high coefficient of expansion. The movable element in this case may comprise a tube of soft iron filled with the wax, the tube being of oval section so as to follow the expansion of the wax. An alternative means for temperature correction consists in arranging the scale so as to be movable by means of a blade made of two parts having different coefficients of expansion. The movable system may consist of a copper tube, in which case the apparatus may act also as a frequency meter.